It has previously been proposed--see the referenced U.S. Pat. No. 4,389,994, DENZ et al, assigned to the assignee of the present application--to control an ICE by changing the operating conditions of the engine in the sense of changing the fuel-air mixture towards a richer mixture and/or changing the ignition timing instant by retarding the spark if knocking or a tendency to knock is being sensed. The control system there disclosed operates electronically. Control of the operation of the engine is obtained by interrogating a memory which stores characteristic data, functions or tables, or tabular fields which relate then existing operating conditions of the engine to knocking or tendency to knock, and, additionally, which relate respective operating conditions of the engines with respect to each other, such as, for example, relationships of engine temperature to loading, speed, or other operating parameters of the engine. The functions or tables interrelating the various parameters and conditions are so arranged that the engine will operate at or close to, preferably just below, knocking conditions. The operating parameter of the engine can be controlled for various desirable functional conditions, for example for maximum torque, maximum power, or optimum exhaust gas composition. Under the desired operating condition, then, the engine should be operated close to the knocking limit thereof.
The data relating to the characteristics of the engine, that is, which relate the respective operating conditions to knocking, for example, or the operating conditions with respect to each other, just under the knocking limit, are usually derived empirically, supplied by the manufacturer of the engine, and are obtained by running the engine under experimental conditions on an engine test stand. In use, and as the engine wears, components age, or are changed, valves and their adjustment change, the fuel quality changes and differs from that under which the tests were made, it is possible that the actual operating conditions or functional relationships under which the engine will operate at a given time will no longer match those from the engine under test, and on which the functional relationships and tables are based. Air pressure, ambient humidity and the like further can change the operating conditions of the engine. Consequently, the tabular data on which the functional relationships are based, and which are stored in a memory, typically a read-only memory (ROM), no longer may fit the engine, and are less than ideally suited to its control.